1. Field of the Invention
This invention relates generally to electronic circuits used in automatic test equipment, and relates more particularly to a tri-state driver circuit for selectively driving a node of a device under test by applying and switching between two reference voltages, and for selectively operating at a high impedance output state.
2. Description of the Prior Art
In automatic test equipment used for testing electronic circuits, electronic signals are generated and applied to selected input pins of the device under test. The condition of the output pins of the device under test is then detected and compared with a desired condition to determine the functionality or quality of the circuit. The circuit within the automatic test equipment which drives the pins of the device under test is commonly referred to as the driver circuit.
Because of the wide variety of electronic circuits which must be tested using the same test equipment, it is desirable for the automatic test equipment to be flexible in permitting the high speed switching of a wide range of voltages onto the input pins of the device under test. Accordingly, the driver circuits for such test equipment must generate output signals with a wide range of voltages and rapidly switch these voltages onto the input pins of the device under test. Prior art test equipment typically could supply output signals at small voltage swings of perhaps one or two volts between high and low voltages, or at large voltage swings of perhaps ten volts, but not both. Prior art test equipment has, thus, been unable to rapidly switch driving signals over a range that includes both small and large voltage swings.